Development of a Nursery Heating System to Increase the Production and Availability of Seed for the BC Shellfish Aquaculture Industry

Final Report
Island Scallops Ltd
AIMAP 2012-P05

Executive Summary

Securing a stable supply of seed is a major constraint to continued development of the British Columbia shellfish aquaculture industry. Currently, BC shellfish farmers rely on US sources of seed; BC shellfish hatcheries are generally unable to compete with the price and timing ofavailability of US seed due to BC's temperate location and the high cost of heating seawater.

As BC's largest marine hatchery, Island Scallops Ltd (ISL) in Qualicum Beach is one of the major suppliers of seed for the BC shellfish industry. The hatchery has traditionally used propane for heating seawater, which is not economically feasible over the winter months, especially in outdoor nursery facilities. The objective of the current project was to develop a system for reducing the cost of heating seawater in the outdoor nursery in order to increase the availability of seed at a competitive price earlier in the growing season.

The new nursery heating system comprised a custom solar collector array with programmable temperature control to heat the seawater in combination with a custom pond cover to help retain the heat. The system was installed and tested over the fall and winter of 2012/2013 and evaluated in comparison with ponds without the system. The project addressed the overall AIMAP goal of improving competitiveness of the Canadian aquaculture industry by 1) stabilizing the supply of seed for BC shellfish farmers and 2) allowing BC hatcheries to compete with US sources of seed.

The project represents innovation that will lead to reduced production costs and increased production of both established cultured species (i.e., oysters and Manila clams) and alternate species (i.e., scallops, geoducks, and mussels). The project contributes to environmental performance of the industry through introduction of a system that improves energy utilization.

Successful development of the nursery heating system benefits not only the company through sales of seed and increased jobs but also the entire BC shellfish farming sector due to the industry-wide need for a stable supply of seed. This contributes to sustainability of the aquaculture industry. As one of the largest seed producers in BC, ISL is in an excellent position to integrate project results into commercial operations.

Introduction

The shortage of seed has been a significant limitation to development of the BC shellfish aquaculture industry. Some natural collection of wild seed occurs for species such as oysters, but for the most part the industry relies on hatchery-produced seed. In BC, shellfish farmers must obtain seed in the spring in order to take advantage of the summer growing season; if seed is put into the ocean at a small size later in the year, then mortality over the winter can be significant. For hatcheries in BC, this means that seed production must occur during the late winter and early spring. At this time of year, seawater must be heated to grow the seed, which can be prohibitively expensive. Consequently, most BC growers rely on US hatcheries that can supply seed at a competitive price in the spring and early summer. This is particularly true for Pacific oysters and Manila clams, which currently account for over 91% of cultured shellfish production in BC. These species are not indigenous to BC and require relatively warm temperatures to grow. The production of oyster and clam seed in BC can require heating seawater even during the summer months. Consequently, millions of oyster and clam seed are imported into the province every year.

Other shellfish such as the hybrid Pacific scallop and the native geoduck clam and blue mussel can be reared at lower temperatures. However, hatchery production of these species also requires heating seawater so that the seed is available to farmers early in the growing season. Furthermore, seed of alternate species (i.e., the Pacific scallop) may not be available to import from foreign sources, or importation may be restricted (i.e., the native geoduck clam) in order to preserve population genetics. This further limits development of shellfish farming in BC.

The shortage of shellfish seed and dependence on US sources was the main problem addressed in the project. Issues associated with relying on US suppliers include seed shortages in the US, vulnerability to trade and regulatory issues, and fluctuating exchange rate.

Island Scallops' hatchery in Qualicum Beach has the capacity to produce significant quantities of seed of several species of shellfish for the BC aquaculture industry. Outdoor nursery ponds range from 250,000 L to 750,000 L in volume and total over 3.5 million L capacity. Production has been focused on Pacific scallop seed for grow out at company farms and sales to other growers, as well as geoduck seed for sales to growers in BC and Washington State. Oyster larvae and seed have been produced on a regular basis, but only in the late spring and summer when ambient seawater temperatures are higher and heating costs lower. In 2011, an exceptionally cold spring caused a delay in oyster production of over one month, resulting in the loss of sales. Development of an economically feasible method of heating seawater at ISL was a priority in order to increase seed production and reduce operational costs. This was essential to supply competitively-priced seed to the BC industry.

Traditionally, the primary source of heat for hatchery operations was a propane boiler, which was both expensive and inefficient for the outdoor nursery where much of the heat escapes from exposed ponds when the air temperature is low. The specific goal of the project was to test a custom-built nursery heating system that combined a more cost-effective and energy-efficient method of heating seawater (a solar collector array with programmable temperature control) with a means of retaining the heat (a custom pond covering).

The project goal was consistent with the AIMAP goal of adopting innovative technologies to improve the competitiveness of the BC aquaculture industry, and fit the following AIMAP innovation priorities:

Sustainable production
Development of a nursery heating system increases seed production and therefore seed supply for the shellfish industry by extending the hatchery production season. Adopting the new system also reduces production costs through savings in energy expenditures. Improving the availability and stability of a domestic seed supply contributes to sustainability of the shellfish industry.

Green technology
Application of solar technology enhances environmental performance by improving energy utilization.

Increased Diversification
The nursery heating system allows increased production of not only existing commercial species (oysters and clams) but also alternate species (scallops, geoducks, and mussels).

Methodology and Results

Island Scallops investigated several options and sources of solar panels and pond covers for development of the nursery heating system. There are basically two types of solar collectors used for heating: flat plate and evacuated tubes. Flat panels are the most common type, have been around much longer, and are less expensive. However, evacuated tubes were chosen for the project for several reasons, including:

• evacuated tubes yield more energy under cloudy conditions and low ambient temperatures (e.g., during winter) than flat plate collectors
• evacuated tube systems are more efficient per square meter than equivalent flat plate systems, reducing the footprint required
• evacuated tubes can be replaced individually without shutting down the entire system, and there is no condensation or corrosion within the tubes

The evacuated tube collectors were sourced from China for the project since the price was significantly less than from any local supplier. Specific requirements were supplied directly to the manufacturer in order to determine the most suitable solar collector and the quantity required.

These criteria included:

• heating seawater from about 8ºC to as high as 18ºC
• handling a seawater flow rate of 400 L/min for 8 hours per day, or 192,000 L daily
• operating in air temperatures that average -5ºC to +5ºC during the winter

Installation of the solar collector system was delayed due to unforeseen delays in receiving components from China and challenges experienced in installing the system. However, the system was fully functional for testing by late winter. One of the technical challenges associated with using a large number of solar collectors under widely varying weather conditions was providing heated seawater to the nursery pond at a
consistent temperature and rate. This was addressed by connecting an insulated 50,000-L reservoir to the solar collectors to store and re-circulate solar-heated fresh water. A titanium heat exchanger was connected to the reservoir to transfer heat from the warmed freshwater to the cold seawater, which was then pumped to the nursery pond. During the day, this system yielded seawater heated to 30ºC at a rate of 120 L/min. The temperature in the reservoir initially fluctuated widely but typically exceeded 50ºC on sunny days.

To better understand and mitigate fluctuations, a temperature logger was used to record temperature in the reservoir at 15-min intervals over 35 days in early spring 2013. During this time, the temperature ranged from a low of 8.8ºC to a high of 57.9ºC and averaged 31.0 ±10.68ºC (n=3250). The mean daily maximum was 40.5 ± 10.92ºC and the mean daily minimum was 22.1 ± 7.42ºC.

There were two main reasons for the large temperature fluctuations in the reservoir. Firstly, despite the insulation some heat was lost when air temperatures were low. Also, the solar collectors were not efficient at night. This problem was addressed by 1) installing a photovoltaic switch to automatically shut down circulation of water from the solar collectors to the reservoir at night and 2) installing a 330,000 BTU boiler to automatically heat water in the reservoir when the temperature reached a pre-set level on cold nights or cloudy days.

Another problem was loss of heat through the heat exchanger; the temperature of the seawater coming out of the exchanger was generally about 20ºC lower than that in the reservoir. Further refinements, including installation of a larger heat exchanger and better temperature controlsystem, are required to improve the operation and increase the efficiency and output of the seawater heating system.

Despite these challenges, the solar collector system effectively supplied solar-heated water and reduced the requirement for propane-heated water for the nursery. To retain the heat in the nursery pond, the challenge was to find an economical cover that could span a significant distance and withstand weather extremes including snow. Initially, a doublelayer canopy composed of two layers of 6-mil polyethylene was installed over the nursery pond, which was 43 m long and 20 m wide and had a volume of about 700,000 L. However, problems with the cover arose during the first major windstorm of the season, so it was replaced with a stronger material – polyethylene “Panda” sheeting that is white on one side (facing upwards to reflect light) and black on the other (facing downward to block light). This material successfully withstood the remaining winter storms and has the added advantage of reducing algae growth in the pond due to the lack of light. Another technical challenge was the method of securing the cover since the ISL nursery islocated on ground with high peat content. The plan was to use helical anchors, but a design modification was made to accommodate wider spans and to improve attachment of the cover by supplementing the helical anchors with a cement foundation. To determine the effect of the cover on heat retention, the temperature in an uncovered pond was compared with that in a covered pond over several weeks in the early spring. Both ponds received a continuous supply of ambient seawater and the temperatures were monitored daily. The temperature in the covered pond was consistently 2-3ºC higher than in the uncovered pond, demonstrating that the cover had a significant effect on maintaining heat in the pond seawater.

The covered pond was successfully tested under commercial conditions for the production of scallop seed in early 2013. Scallop larvae produced at the ISL hatchery were added to the pond in the late winter and by early spring, about 30 days later, some of the seed had reached a size large enough (~1 mm) to be transferred to the ocean for on-growing. This is relatively early for ocean entry of hatchery-produced seed.

Going Forward

Despite several challenges and issues, the new nursery heating system was uccessfully integrated into commercial production by the end of the project. Further refinements are required to improve operation of the system, especially in the areas of heat exchange and temperature control, and to increase output. Propane is still required to supplement the solar collectors for heating seawater overnight and during periods of low temperature, so future innovations should focus on increasing the overall efficiency of the system and reducing the cost of heating the nursery.

Conclusion

The results of the project have a positive economic impact on Island Scallops through enhanced production and reduced operational costs. The custom-built nursery heating system effectively combines an economical, energy-efficient method of heating seawater (the solar collector array) with a means of retaining the heat (a custom pond covering) and shows significant potential for further commercial development.

Extending the production season at the hatchery also creates employment as hatchery and nursery operations are extended; an estimated four direct jobs were created by installation of the new nursery system and several temporary jobs were created during the construction phase.